The Snow Dragon icebreaker (left, far background) is seen from the bridge of the Aurora Australis ship off Antarctica.

The icebreaker Aurora Australis had been slowly cracking through thick ice toward open water after a Chinese helicopter on Thursday plucked the passengers from their stranded Russian research ship and carried them to the Aurora.

But on Friday afternoon, the crew of the Chinese icebreaker that had provided the helicopter said they were worried about their own ship's ability to move through the ice. The Snow Dragon, which is at the edge of the ice pack surrounding the Russian vessel, reported that an attempt to move through the ice early Saturday morning had failed, according to the Australian Maritime Safety Authority's Rescue Coordination Centre, which oversaw the rescue.

The Aurora — which was carrying the passengers to the Australian island state of Tasmania — was initially told to stay in the area in case the Snow Dragon needed help, but on Saturday was released from that duty, the authority said.

The agency said there was no danger to anyone on board the Snow Dragon, which reported having several weeks of food supplies on board. But it was yet another wrinkle in the highly complex rescue operation of those on board the Russian ship MV Akademik Shokalskiy, which got stuck in the ice on Christmas Eve.

A spot of clear weather on Thursday finally allowed the multinational rescue operation after blinding snow, strong winds and thick sea ice forced rescuers to turn back time and again.

More than 50 passengers from a Russian research ship were airlifted to safety after ice stranded their vessel. NBC's Martin Fletcher reports.

The twin-rotor helicopter, which is based on the Snow Dragon, took seven hours to carry the scientists and tourists in groups of 12 from the Russian ship to the Aurora.

The 22 crew members of the Akademik Shokalskiy stayed with that icebound vessel, which is not in any danger and has enough supplies to last for weeks. They will wait until the ice surrounding the ship breaks up, which could take several weeks, ASMA Emergency Response Division manager John Young said.

The Akademik Shokalskiy, which left New Zealand on Nov. 28, got stuck after a blizzard pushed the sea ice around the ship, freezing it in place about 1,700 miles south of Hobart, Tasmania. The scientific team on board the Russian vessel had been recreating Australian explorer Douglas Mawson's 1911 to 1913 voyage to Antarctica.

After being rescued by a Chinese helicopter, the 52 scientists and tourists aboard the Russian vessel that's been trapped in Antarctic ice are now waiting again, aboard an Australian icebreaker, before making their journey back to land. The ship has been told to stop its journey home because a Chinese vessel involved in the rescue is concerned that it, too, may get stuck in heavy sea ice, necessitating further evacuations.